Network Working Group Dan Li
Huiying Xu
Huawei
Snigdho Bardalai
Fujitsu
Julien Meuric
France Telecom
Diego Caviglia
Ericsson
Internet Draft
Category: Standards Track
Expires: August 2008 February 20, 2008
Data Channel Status Confirmation Extensionsfor the Link Management Protocoldraft-li-ccamp-confirm-data-channel-status-03.txt
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Abstract
This document defines simple additions to the Link Management
Protocol (LMP) to provide a control plane tool that can assist in the
location of stranded resources by allowing adjacent LSRs to confirm
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A data channel status mismatch exists if the LSR at one end of a TE
link believes that the data channel is assigned to carry data, but
the LSR at the other end does not. The term "ready to carry data"
means cross-connected or bound to an end-point for the receipt or
delivery of data.
Data channel mismatches cannot be detected from the TE information
advertised by the routing protocols [RFC4203], [RFC4205]. The
existence of some data channel mismatch problems may be detected by
a mismatch in the advertised bandwidths where bidirectional TE links
and bidirectional services are in use, but where unidirectional
services exist, or where multiple data channel mismatches occur, it
is not possible to detect such errors through the routing protocol-
advertised TE information. In any case, there is no mechanism to
isolate the mismatches by determining which data channels are at
fault.
If a data channel mismatch exists, any attempt to use the data
channel for a new LSP will fail. One end of the TE link may attempt
to assign the TE link for use, but the other end will report the data
channel as unavailable when the control plane or management plane
attempts to assign it to an LSP.
Although such a situation can be resolved through the use of the
Acceptable Label Set object in GMPLS signaling [RFC3473], such a
procedure is inefficient since it may require an additional signaling
exchange for each LSP that is set up. When many LSPs are to be set
up, and when there are many data channel mismatches, such
inefficiencies become significant. It is desirable to avoid the
additional signaling overhead, and to report the problems to the
management plane so that they can be resolved to improve the
efficiency of LSP setup.
Correspondingly, such a mismatch situation may give rise to
misconnections in the data plane especially when LSPs are set up
using management plane operations.
Resources (data channels) that are in a mismatched state are often
described as "stranded resources". They are not in use for any LSP,
but they cannot be assigned for use by a new LSP because they appear
to be in use. Although it is theoretically possible for management
plane applications to audit all network resources to locate stranded
resources and to release them, this process is rarely performed
because of the difficulty of coordinating different Element
Management Systems (EMSs), and the associated risks of accidentally
releasing in-use resources. It is desirable to have a control plane
mechanism that detects and reports stranded resources.
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This document defines simple additions to the Link Management
Protocol (LMP) [RFC4204] to provide a control plane tool that can
assist in the location of stranded resources by allowing adjacent
LSRs to confirm data channel statuses, and provides triggers for
notifying the management plane if any discrepancies are found.
2. Problem Explanation
Examples of data channel mismatches are described in the following
three scenarios.
In all of the scenarios, the specific channel resource of a data link
will be unavailable because of the data channel status mismatch, and
this channel resource will be wasted. Furthermore, a data channel
status mismatch may reduce the possibility of successful LSP
establishment, because a data channel status mismatch may result in
failure when establishing an LSP.
So it is desirable to confirm the data channel statuses as early as
possible.
2.1. Mismatch Caused by Manual Configuration
The operator may have configured a cross-connect at only one end of
a TE link using an EMS. The resource at one end of the data channel
is allocated, but the corresponding resource is still available at
the other end of the same data channel. In this case, the data
channel may appear to be available for use by the control plane
when viewed from one end of the TE link, but will be considered to
be unavailable by the other end of the TE link. Alternatively, the
available end of the data channel may be cross-connected by the
management plane and a misconnection may result from the fact that
the other end of the data channel is already cross-connected.
Figure 1 shows a data channel between nodes A and B. The resource at
A's end of the TE link is allocated through manual configuration,
while the resource at B's end of the TE link available, so the data
channel status is mismatched.
allocated available
+-+------------+-+
A |x| | | B
+-+------------+-+
data channel
Figure 1. Mismatch caused by manual configuration
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draft-li-ccamp-confirm-data-channel-status-03.txt February 20082.2. Mismatch Caused by LSP Deletion
The channel status of a data link may become mismatched during the
LSP deletion process. If the LSP deletion process is aborted in the
middle of the process (perhaps because of a temporary control plane
failure), the cross-connect at the upstream node may be removed while
the downstream node still keeps its cross-connect, if the LSP
deletion was initiated by the source node.
For example, in Figure 2 an LSP traverses nodes A, B, and C. Node B
resets abnormally when the LSP is being deleted. This results in the
cross-connects of node A and C being removed, but the cross-connect
of node B still being in use. So the data channel statuses between
nodes A and B, and between nodes B and C are both mismatched.
<---------LSP--------->
+-+-------+-+-------+-+
| | |X| | |
+-+-------+-+-------+-+
A B C
Figure 2. Mismatch caused by LSP deletion
RSVP-TE restart processes [RFC3473], [RFC5063] define mechanisms
where adjacent LSRs may resynchronize their control plane state to
reinstate information about LSPs that have persisted in the data
plane. The mechanisms allow LSRs to detect mismatched data plane
state after the expiry of the Recovery Timer. It is a local policy
decision how this mismatched state is handled. Some deployments may
decide to automatically clean up the data plane state so it matches
the control plane state, but others may choose to raise an alert to
the management plane and leave the data plane untouched just in case
it is in use.
In such cases, data channel mismatches may arise after restart and
might not be cleared up by the restart procedures.
2.3. Manual Change of the Cross-Connect State
In transport nodes it is possible to perform certain manual
operations on a cross-connect such as forced protection switch,
red-line, etc. These operations will make it impossible to release
the cross-connect when an LSP is being deleted.
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draft-li-ccamp-confirm-data-channel-status-03.txt February 20082.4. Failed Resources
Even if the situation is not common, it might happen that a
termination point of a TE-link is seen as failed by one end, while on
the other end it is seen as OK. This problem may arise due to some
failure either in the hardware or in the status detection of the
termination point.
This mismatch in the termination point status can lead to failure in
case of bidirectional LSP set-up.
Good Failed
+-+------------+-+
A | | |X| B
+-+------------+-+
data channel
Path Message with Upstream Label---->
Figure 3. Mismatch caused by resource failure
In this case upstream node chooses to use termination point A in
order to receive traffic from downstream node. From the upstream's
point of view, the resource is available thus usable; however, in the
downstream node, the corresponding termination point (resource B) is
broken. This leads to a set-up failure.
3. Motivation
The requirement does not come from a lack in GMPLS specifications
themselves but rather from operational concerns because, in most
cases, GMPLS-controlled networks will co-exist with legacy networks
and legacy procedures.
The protocol extensions are intended to detect data plane problems
resulting from mis-use or mis-configurations triggered by user error,
or resulting from failure to clean up the data plane after control
plane disconnection. It is anticipated that human mistake is probably
the major factor to deal with. It is not the intention to provide a
protocol mechanism to deal with broken implementations.
The procedures defined in this document are designed to be operated
on a periodic or on-demand basis. It is NOT RECOMMENDED that the
procedures be used to provide a continuous and on-line monitoring
process.
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As LMP is already used to verify data plane connectivity, it is
considered to be an appropriate candidate to support this feature.
4. Extensions to LMP
A control plane tool to detect and isolate data channel mismatches is
provided in this document by simple additions to the Link Management
Protocol (LMP) [RFC4204]. It can assist in the location of stranded
resources by allowing adjacent LSRs to confirm data channel statuses.
Outline procedures are described in this section. More detailed
procedures are found in Section 5.
4.1. Confirm Data Channel Status Messages
Extensions to LMP to confirm a data channel status are described
below. In order to confirm a data channel status, the new LMP
messages are sent between adjacent nodes periodically or driven by
some event (such as an operator command, a configurable timer, or the
rejection of an LSP setup message because of an unavailable
resource).
Three new messages are defined to check data channel status. Message
Type numbers are found in Section 7.1.
4.1.1. ConfirmDataChannelStatus Messages
The ConfirmDataChannelStatus message is used to tell the remote end
of the data channel what the status of the local end of the data
channel is, and to ask the remote end to report its data channel. The
message may report on (and request information about) more than one
data channel.
<ConfirmDataChannelStatus Message> ::= <Common Header>
<LOCAL_LINK_ID>
<MESSAGE_ID>
<DATA_LINK>[<DATA_LINK>...]
When a node receives the ConfirmDataChannelStatus message, and the
data channel status confirmation procedure is supported at the node,
the node compares its own data channel statuses with all of the data
channel statuses sent by the remote end in the
ConfirmDataChannelStatus message. If a data channel status mismatch
is found, this mismatch result SHOULD be reported to the management
plane for further action. Management plane reporting procedures and
actions are outside the scope of this document.
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draft-li-ccamp-confirm-data-channel-status-03.txt February 20084.1.2. ConfirmDataChannelStatusAck Messages
The ConfirmDataChannelStatusAck message is sent back to the node
which originated the ConfirmDataChannelStatus message to return the
requested data channel statuses.
When the ConfirmDataChannelStatusAck message is received, the node
compares the received data channel statuses at the remote end with
those at the local end (the same operation as performed by the
receiver of the ConfirmDataChannelStatus message). If a data channel
status mismatch is found, the mismatch result SHOULD be reported to
the management plane for further action.
<ConfirmDataChannelStatusAck Message> ::= <Common Header>
<MESSAGE_ID_ACK>
<DATA_LINK>[<DATA_LINK>...]
The contents of the MESSAGE_ID_ACK objects MUST be obtained from the
ConfirmDataChannelStatus message being acknowledged.
Note that the ConfirmDataChannelStatusAck message is used both when
the data channel statuses match and when they do not match.
4.1.3. ConfirmDataChannelStatusNack Messages
When a node receives the ConfirmDataChannelStatus message, if the
data channel status confirmation procedure is not supported but the
message is recognized, a ConfirmDataChannelStatusNack message
containing an ERROR_CODE indicating "Channel Status Confirmation
Procedure not supported" MUST be sent.
If the data channel status confirmation procedure is supported, but
the node is unable to begin the procedure, a
ConfirmDataChannelStatusNack message containing an ERROR_CODE
indicating "Unwilling to Confirm" MUST be sent. If a
ConfirmDataChannelStatusNack message is received with such an
ERROR_CODE, the node which originated the ConfirmDataChannelStatus
message MAY schedule the ConfirmDataChannelStatus message
retransmission after a configured time. A default value of 10 minutes
is RECOMMENDED for this timer.
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<ConfirmDataChannelStatusNack Message> ::= <Common Header>
[<LOCAL_LINK_ID>]
<MESSAGE_ID_ACK>
<ERROR_CODE>
The contents of the MESSAGE_ID_ACK objects MUST be obtained from the
ConfirmDataChannelStatus message being rejected.
4.2. Data Channel Status Subobject
A new Data Channel Status subobject type is introduced to the DATA
LINK object to hold the data channel status and Data Channel
Identification.
See Section 7.2 for the Subobject Type value.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Data Channel Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Data Channel ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Data Channel Status:
This is a series of bit flags to indicate the status of the data
channel. The following values are defined.
0x0000 : The channel is available/free.
0x0001 : The channel is cross-connected/allocated.
Data Channel ID
This identifies the data channel. The length of this field can be
deduced from the Length field in the subobject. Note that all
subobjects must be padded to a four byte boundary with trailing
zeros. If such padding is required, the Length field MUST indicate
the length of the subobject up to, but not including, the first
byte of padding. Thus, the amount of padding is deduced and not
represented in the Length field.
Note that the Data Channel ID is given in the context of the sender
of the ConfirmChannelStatus message.
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The data-channel ID must be encoded as a label value. Based on the
type of signal e.g. SONET/SDH, Lambda etc. the encoding methodology
used will be different. For SONET/SDH the label value is encoded as
per RFC4606.
5. Procedures
The data channel status confirmation related LMP messages are sent
between adjacent nodes periodically or driven by some events to
confirm the channel status for the data links. The procedure is
described below:
. The SENDER constructs a ConfirmDataChannelStatus message which
contains one or more DATA_LINK objects. Each DATA_LINK object
contains one or more Data Channel Status subobject. The Data
Channel ID field in the Data Channel Status subobject indicates
which data channel needs to be confirmed, and reports the data
channel status at the SENDER. The ConfirmDataChannelStatus message
is sent to the RECEIVER.
. The RECEIVER extracts the data channel statuses from the
ConfirmDataChannelStatus message, and compares these with its data
channel statuses for the reported data channels. If a data channel
status mismatch is found, the mismatch result SHOULD be reported
to the management plane for further action. The RECEIVER also
sends the ConfirmDataChannelStatusAck message which carries all
the local end statuses of the requested data channels to the
SENDER.
. If the RECEIVER is not able to support or to begin the
confirmation procedure, the ConfirmDataChannelStatusNack message
MUST be responded with the ERROR_CODE which indicates the reason
of rejection.
. The SENDER receives the response ConfirmDataChannelStatusAck
message, and compares the received data channel statuses at the
remote end with the data channel statuses at the local end. If a
data channel status mismatch is found, the mismatch result SHOULD
be reported to the management plane for further action.
. The ConfirmDataChannelStatus message SHOULD be resent, if the
ConfirmDataChannelStatusNack message is received or no response
message is received in the configured time by the SENDER.
The data channel status mismatch results MAY be stored, and this
information MAY be queried in the future.
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The data channel status mismatch issue warned about by LMP may be
automatically resolved by RSVP restart. For example, the restarting
node may also have damaged its data plane. This leaves the data
channels mismatched. But RSVP restart will re-install the data plane
state in the restarting node.
6. Security Considerations
[RFC4204] describes how LMP messages between peers can be secured,
and these measures are equally applicable to the new messages defined
in this document.
The operation of the procedures described in this document does not
of themselves constitute a security risk since they do not cause any
change in network state. It would be possible, if the messages were
intercepted or spoofed to cause bogus alerts in the management plane
and so the use of the LMP security measures are RECOMMENDED.
Note that operating the procedures described in this document may
provide a useful additional security measure to verify that data
channels have not been illicitly modified.
7. IANA Considerations7.1. LMP Message Types
IANA maintains the "Link Management Protocol (LMP)" registry which
has a subregistry called "LMP Message Type". IANA is requested to
make three new allocations from this registry as follows. The message
type values are suggested and to be confirmed by IANA.
Value Description
------ ---------------------------------
21 ConfirmDataChannelStatus
22 ConfirmDataChannelStatusAck
23 ConfirmDataChannelStatusNack
7.2. LMP Data Link Object Subobject
IANA maintains the "Link Management Protocol (LMP)" registry which
has a subregistry called "LMP Object Class name space and Class type
(C-Type)". This subregistry has an entry for the DATA_LINK object,
and there is a further embedded registry called "DATA_LINK Sub-object
Class name space". IANA is requested to make the following allocation
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Julien Meuric
France Telecom
2, avenue Pierre Marzin
22307 Lannion Cedex
France
Phone: +33 2 96 05 28 28
Email: julien.meuric@orange-ftgroup.com
Diego Caviglia
Ericsson
Via A. Negrone 1/A 16153
Genoa Italy
Phone: +39 010 600 3736
Email: diego.caviglia@ericsson.com
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